Work in our laboratory has focused on the nature of the immunomodulatory effects of bacterial lipopolysaccharide. We shall continue to investigate the role of regulatory T cells and accessory macrophages in LPS stimulatory and inhibitory effects in the antibody response in vivo and in vitro, utilizing syngeneic LPS responder and non-responder strains of mice. In addition, we are examining the ability of lipid-A associated protein and muramyl dipeptide, both bacterial cell wall constituents with adjuvant properties, to exert suppressive and stimulatory effects on the antibody response in LPS non-responder strains of mice. Finally, we shall characterize and determine the cellular requirements for the synergy we have observed between LPS and T cell replacing factors in CBA/N mice, a strain with B cell maturational defects and the absence of a B cell surface antigen which is involved in B cell triggering.